Introduction
The Urine Output Calculator helps you find out how fast the kidneys are making urine. It takes a patient's weight, total urine collected, and the number of hours it was collected over, then gives you a rate in mL/kg/hr. This rate is one of the quickest ways doctors and nurses check if the kidneys are working well.
Healthy adults produce roughly 800–2,000 mL of urine per day on a normal fluid intake of about 2 liters.4 For a typical adult that works out to about 0.5 to 1.0 mL/kg/hr. When the rate drops below 0.5 mL/kg/hr for six hours or more, it meets the standard definition of acute kidney injury (AKI).3 Catching a low urine output early matters because the sooner the care team acts, the better the chance of protecting the kidneys from lasting damage.
This calculator does three things at once. First, it computes your urine output rate. Second, it projects that rate to a full 24-hour output so you can compare it to standard daily ranges. Third, if you enter fluid intake, it shows your fluid balance: whether the body is holding onto fluid or losing more than it takes in. The tool also flags results using the RIFLE criteria, a widely used scale that sorts kidney injury into Risk, Injury, and Failure stages based on urine output duration.
Simply enter the patient's weight, total urine volume, and collection time, then press Calculate to see instant results, a step-by-step breakdown of the math, and a visual chart comparing the rate to clinical thresholds.
How to Use Our Urine Output Calculator
Enter your patient's weight, urine volume, and collection time below. The calculator will return the urine output rate in mL/kg/hr, a projected 24-hour output, fluid balance, and a clinical interpretation based on RIFLE criteria.
Weight: Type the patient's body weight. Use the toggle to switch between kilograms (kg) and pounds (lbs). The calculator will convert pounds to kilograms for you.
Total Urine Output: Enter the total amount of urine collected during the measurement period, in milliliters (mL). This is the full volume measured, not a per-hour amount.
Time Period: Enter the number of hours over which the urine was collected. The standard collection window is 24 hours, but you can enter any duration from just above 0 up to 72 hours.
Fluid Intake: This field is optional. Enter the total fluid the patient drank or received during the same time period, in milliliters. If filled in, the calculator will show the net fluid balance: whether the patient retained or lost fluid overall. Leave it blank to skip this step.
Press Calculate to see your results. Press Reset to clear all fields and start over.
What Is Urine Output and Why Does It Matter?
Urine output is the amount of urine your body makes over a set period of time. It is one of the easiest ways doctors and nurses check how well your kidneys are working. Healthy kidneys filter waste and extra water from your blood and turn it into urine. When your kidneys slow down or stop working, urine output drops. That is why tracking it is so important in hospitals and clinics.
How Urine Output Is Measured
Urine output rate is measured in mL/kg/hr, which means milliliters of urine per kilogram of body weight per hour. To find this number, you divide the total urine volume by the patient's weight and then divide again by the number of hours collected. This calculator does that math for you instantly.
What Is Normal Urine Output?
For adults, output below 0.5 mL/kg/hr sustained for hours is the threshold used to define acute kidney injury.3 Typical output is about 0.5 to 1.0 mL/kg/hr. Over a full day, a normal 24-hour urine volume is roughly 800 to 2,000 mL with a fluid intake of about 2 liters.4 This calculator flags output above 2,000 mL/day as polyuria. Definitions vary; MedlinePlus puts the adult threshold at more than 2.5 liters a day.6 Polyuria can be a sign of diabetes, high fluid intake, or other conditions.
Low Urine Output: Oliguria and Anuria
Oliguria means urine output has dropped below 400 mL per day, the traditional definition. For comparison, most adults make at least 500 mL of urine in 24 hours.5 Anuria means the body is making little to no urine at all. Both are warning signs that the kidneys may be in trouble. Causes include dehydration, blood loss, infection, heart failure, or a blockage in the urinary tract. Monitoring blood pressure is also critical in these situations, as adequate kidney perfusion depends on it.
RIFLE Criteria for Acute Kidney Injury
Doctors use the RIFLE criteria to grade how serious a kidney problem is. RIFLE stands for Risk, Injury, Failure, Loss, and End-stage.2 This calculator uses the urine output part of those criteria:
- Risk: Output below 0.5 mL/kg/hr for more than 6 hours.1
- Injury: Output below 0.5 mL/kg/hr for more than 12 hours.1
- Failure: Output below 0.3 mL/kg/hr for more than 24 hours, or no urine at all for more than 12 hours.1
Catching these stages early gives doctors the best chance to protect the kidneys and treat the cause. Alongside urine output, clinicians often check related lab values such as the anion gap, corrected calcium, and serum osmolality to build a full picture of kidney and metabolic function.
Fluid Balance
Fluid balance compares how much fluid a person drinks (or receives through an IV) to how much urine they produce. A positive balance means the body is holding on to extra fluid, which can cause swelling. A negative balance means the body is losing more fluid than it takes in, which can lead to dehydration. This calculator shows your fluid balance when you enter a fluid intake value.